1. Technical Field
This disclosure relates to exhaust gas recirculation (EGR) systems and in particular to an EGR assembly combining EGR flow control and EGR cooling.
2. Background Art
EGR systems are used to recirculate part of the exhaust gas produced by an internal combustion engine, of a vehicle for example, to suppress the generation of nitrogen oxides. EGR systems may incorporate an EGR cooler, a bypass of the EGR cooler, and an EGR valve. See for example EP-A-1933023 which describes a water-cooled, in-line EGR cooler comprising a cylindrical shell.
GB 2062749 A describes an EGR cooler which has the form of a U-shaped tube and is adapted to be mounted directly onto an engine intake manifold.
One known type of EGR valve for regulating the flow of recirculated exhaust gas is described in EP 1918 566. This type of valve, often known as a poppet valve, is electrically controllable in accordance with engine operating conditions. The term ‘EGR valve’ as meant herein is a poppet valve.
FIGS. 1A and 1B illustrate two alternative arrangements of a known EGR circuit.
In FIG. 1A, a portion of the exhaust gas from an internal combustion engine is directed from the exhaust manifold region 1 to the inlet manifold region 2, via an in-line EGR cooler 3. An EGR valve 4 is positioned on the hot side of the cooler and regulates EGR flow. An EGR cooler is provided to cool the hot exhaust gases to reduce NOx formation even further. A butterfly valve 5 deflects EGR gas either through the cooler 3 or around a bypass link 6. A problem with this arrangement is that as the valve 4 is always cooled, it cools the EGR gas flowing through it, even when engine operating conditions dictate that there is no requirement for the EGR gas to be cooled prior to reaching the intake manifold. This problem can be overcome by re-positioning the valve 4 as shown in FIG. 1B.
In FIG. 1B, the EGR valve 4 is located on the cold side of the cooler 3. However, any contaminants settling on the valve mechanism tend not to get burned off and the valve 4 eventually starts to stick. A further drawback with both of the above arrangements is that the butterfly valve 5 tends to leak so that either not all of the EGR gas reaching the intake manifold is cooled or else not all the EGR gas bypasses the cooler. Furthermore, butterfly valves are often operated by a vacuum system which can be prone to external contamination, creating premature wear of the actuation system.
An EGR system which mitigates the above disadvantages would be advantageous.